Piezo actuators change their form, for example their length, when they are subjected to an electrical voltage, and can in this process exert significant force on, for example, plungers of valves. They may therefore be used in fuel injection valves where, however, due to the high dynamic performance required, they must be operated with complex end stages and drive concepts.
A further use of a piezo actuator is described in German Patent application DE 10 2006 019 404 A1. There, the piezo actuator operates on the piston face of a pressure reducer operated in a pressure regulator of a CNG-driven motor vehicle (CNG: compressed natural gas). With the help of a piezo actuator acting on the valve of an excess flow mechanism, the gas pressure in the working chamber of the control unit can be changed in a targeted manner. A at the same time the position of the valve of the excess flow mechanism of the pressure reducer can be affected, and its output pressure thereby adjusted to a predetermined setpoint value.
The end stage that is necessary to drive the piezo actuator must be able to statically adjust the voltage at the piezo actuator; on the other hand, low demands are placed on the dynamic performance in comparison with piezo fuel injection valves. The end stage must, however, also be capable of adjusting the voltage precisely even at very low voltages. Since the pressure reducer is in competition with unregulated systems, there is nevertheless a particular pressure on costs.
DC-DC converters, as are described in German Patent application DE 10 2012 204 576 A1, may be considered for the voltage supply or drive of the piezo actuator. The DC-DC converter described there is designed as an H-bridge converter, and an additional dissipative path is provided for discharging the piezo actuator.
As an alternative to this, German Patent application DE 10 2005 016 279 A1 discloses a DC-DC converter that is designed as a flyback converter that is connected on the input side with a capacitor that is fed by a further upstream DC-DC converter. Here again, an additional dissipative path is present for discharging connected piezo actuators.